This invention relates generally to the developing of a latent electrostatic image on copy paper with a toner and the fusing of the toner onto the copy paper in an electrostatic copying machine and more particularly to the developing of the latent electrostatic image using a single component magnetic toner and the fusing of the toner onto the copy paper using pressure.
Since the inception of the single component magnetic toner powder for electrostatic copy machines, a number of devices have been proposed which apply the magnetic toner powder to the latent electrostatic image on electrostatic copy paper. Typical examples of such magnetic toner powder applicators are illustrated in U.S. Pat. Nos. 3,455,276; 3,739,749; and 3,849,161. One problem associated with the prior art magnetic toner applicators is the inability of these applicators to dispense the magnetic toner powder in the proper metered amount and at the proper flow rate to insure accurate and uniform distribution of the magnetic toner powder over the latent electrostatic image to develop same. Another problem associated with these prior art magnetic toner powder applicators is the difficulty encountered in replenishing the supply of magnetic toner powder in the applicator as required.
The magnetic toner powders are also capable of being fused onto the copy paper using pressure to rupture the magnetic toner powder particles and press them into the paper. Different devices have been proposed which use a pair of pressure rolls to apply pressure to the magnetic toner powder particles to rupture them and fuse them onto the paper. Examples of these arrangements are illustrated in U.S. Pat. Nos. 3,269,626; 3,295,497; and 3,846,151. One of the primary problems with these prior art pressure fusing devices is that the pressures required to rupture the magnetic toner powder particles to fuse the particles onto the copy paper causes these prior art fusing devices to produce an undesirable highly smooth finish on the copy paper which is thus highly reflective and therefore makes the copy paper more difficult to read. Another difficulty encountered with these prior art fusing devices is that the toner powder frequently sticks to one of the pressure fusing rolls as an incident to the fusing process to cause the image defined by the magnetic toner particles to offset onto one of the pressure fusing rolls. This has resulted in elaborate attempts to prevent the magnetic toner particles from offseting onto the pressure fusing rolls. Yet another problem associated with prior art pressure fusing devices is that the pressure rollers contacted each other when the copy paper was not between the rollers. This caused problems in feeding the paper between the rollers and also created undesirable noise when the rollers snapped back together after passage of the copy paper therethrough. Further, the metal-to-metal contact between the pressure rollers usually required a greater start-up torque than is available from the normal copy machine drive which necessitated a new separate drive motor for the pressure fusing device.